Implantable heart stimulating device, system and method

ABSTRACT

In an implantable biventricular heart stimulating device, and a biventricular heart stimulating method, wherein operation takes place normally with a time VV between a pacing pulse delivered, or inhibited, by a first ventricular pacing circuit and a pacing pulse delivered, or inhibited, by a second ventricular pacing circuit, and wherein a time VV cts  is determined that is to be used instead of VV during a capture threshold search.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an implantable heart stimulating devicewith which it is possible to stimulate both the ventricles of a heart,i.e. a bi-ventricular pacer.

The invention also relates to a system including such a device and to amethod of, in a human or animal being, performing a capture thresholdsearch.

2. Description of the Prior Art

Several different implantable devices for stimulating a heart are known.The devices are normally able to sense the electrical activity of theheart, Some implantable devices are able to deliver stimulation pulsesto and/or sense the right atrium (in some case even the left atrium) andalso to deliver stimulation pulses to and sense both the left and rightventricle.

Devices that are able to deliver stimulation pulses to both the left andright ventricle can be called bi-ventricular pacers. Such devices can beused to treat patients who suffer from different severe cardiacproblems, e.g. patients suffering from congestive heart failure (CHF).CHF is defined generally as the inability of the heart to deliver asufficient amount of blood to the body. CHF can have different causes.It can for example be caused by a left bundle branch block (LBBB) or aright bundle branch block (RBBB). By using bi-ventricular pacing, thecontraction of the ventricles can be controlled in order to improve theability of the heart to pump blood. The stimulation pulses to the twoventricles can be delivered simultaneously but it is also known that thestimulation pulses to the two ventricles are delivered with a short timedelay between them in order to optimize the pumping performance of theheart.

U.S. Pat. No. 5,720,768 describes different possible electrode positionsin order to stimulate or sense the different chambers of the heart.

U.S. Pat. No. 6,070,100 describes that electrodes may be positioned inboth the left and the right atrium as well as in the left and the rightventricles.

In connection with implantable pacers, it is known to detect the captureof the heart, i.e. to detect whether the heart actually reacts to adelivered stimulation pulse. If the heart is not captured, it ispossible to arrange the pacer to deliver a back-up pulse with a higherpulse energy than the first pulse. It is also possible to increase thepulse energy in future stimulation pulses if capture is not detected. Inorder to save battery it is important that the stimulation pulses arenot delivered with an unnecessarily high energy. In order to determine asuitable pulse energy, it is known to perform an automaticthreshold/capture search. By varying the energy of the stimulationpulses, and by detecting whether capture occurs, it is thus possible tofind a threshold value for the stimulation pulse energy. Based on thethreshold value, a suitable stimulation pulse energy can be determined.

The detection of capture involves several problems. Different signalsfrom the heart or generated by the pacemaker may interfere with eachother, which may make the detection of capture difficult. The evokedresponse that it is intended to detect may thus be hidden because ofother electrical phenomena. It is particularly difficult to detectcapture in a bi-ventricular pacer, since in such a pacer there are moredelivered and detected signals which may interfere with each other.

A phenomenon in this technical field is “fusion”. A fusion may occurwhen an intrinsic depolarization of the heart takes placesimultaneously, or at least almost simultaneously, with a stimulationpulse from the heart stimulating device. Fusion should be avoided whenperforming a threshold/capture search. In order to avoid such fusion, itis known to temporarily, during such a threshold/capture search, shortenthe AV-delay and the PV-delay. Typically, these delays are shortenedsuch that they are set at a predetermined fixed value (e.g. 50 ms and 25ms, respectively) during such a search.

U.S. Pat. No. 6,498,950 describes a device and method for performingautomatic capture/threshold determination in a mono-ventricular pacer.The patent describes a method and a device that instead of using thementioned fixed AV-delay and the PV-delay during a threshold/capturesearch, use delays adapted to the particular patient. According to thispatent, the device periodically measures the AR/PR conduction times andtabulate and/or otherwise process this data. When an automaticcapture/threshold determination occurs, this measured conduction data,which corresponds to the particular patient, is used to adjust the AV/PVdelays while minimizing patient discomfort and adverse hemodynamiceffects.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an implantablebi-ventricular heart stimulating device with which a threshold/capturesearch can be carried in an hemodynamically optimal manner. Anotherobject is to provide such a device with which it is possible to adjustcertain timing parameters in an optimal manner when performing such athreshold/capture search. A further object it to provide such a devicewith which it is possible to deliver ventricular pacing pulses to bothventricles even during the time cycles when such a threshold/capturesearch is carried out. Further objects or advantages of the inventionwill become clear from the following description and claims.

The above objects are achieved by an implantable heart stimulatingdevice including a control circuit comprising:

at least one memory;a first atrial sensing and/or pacing circuit, adapted to communicatewith a first atrial sensing and/or pacing electrode suited to bepositioned in an atrium of a heart, wherein said first atrial sensingand/or pacing circuit is adapted to enable sensing and/or pacing of suchan atrium;a first ventricular sensing circuit, adapted to communicate with a firstventricular sensing electrode suited to be positioned in or at a firstventricle of a heart, wherein said first ventricular sensing circuit isadapted to enable sensing of such a ventricle;a first ventricular pacing circuit, adapted to communicate with a firstventricular pacing electrode suited to be positioned in or at a firstventricle of a heart, wherein said first ventricular pacing circuit isadapted to enable pacing of such a ventricle;a second ventricular sensing circuit, adapted to communicate with asecond ventricular sensing electrode suited to be positioned in or at asecond ventricle of a heart, wherein said second ventricular sensingcircuit is adapted to enable sensing of such a ventricle;a second ventricular pacing circuit, adapted to communicate with asecond ventricular pacing electrode suited to be positioned in or at asecond ventricle of a heart, wherein said second ventricular pacingcircuit is adapted to enable pacing of such a ventricle,said control circuit being arranged to be able to detect an evokedresponse to a pacing pulse delivered by said first ventricular pacingcircuit by sensing, with said first ventricular sensing circuit, withina first time window that follows after a pacing pulse delivered by saidfirst ventricular pacing circuit;said control circuit being arranged to be able to detect an evokedresponse to a pacing pulse delivered by said second ventricular pacingcircuit by sensing, with said second ventricular sensing circuit, withina second time window that follows after a pacing pulse delivered by saidsecond ventricular pacing circuit;said control circuit being arranged to be able to operate with timecycles corresponding to normal heart cycles;said control circuit being arranged to be able to operate, during thenormal operation of the device, with a value PV and/or AV, where PV isthe time between the sensing with said first atrial sensing and/orpacing circuit and a subsequent pacing pulse, which may also beinhibited, of said first ventricular pacing circuit and AV is the timebetween the pacing with said first atrial sensing and/or pacing circuitand a subsequent pacing pulse, which may also be inhibited, of saidfirst ventricular pacing circuit;said control circuit being arranged to, within a time cycle, be able todeliver pacing pulse with both said first ventricular pacing circuit andsaid second ventricular pacing circuit with a time gap VV, during thenormal operation of the device, between a pacing pulse delivered, orinhibited, by said first ventricular pacing circuit and a pacing pulsedelivered, or inhibited, by said second ventricular pacing circuit,wherein said time gap VV is ≧0;said control circuit being arranged to be able to carry out a capturethreshold search, by, during a plurality of time cycles, vary the energyof the pacing pulses delivered by said first ventricular pacing circuitand said second ventricular pacing circuit and to detect, with saidfirst ventricular sensing circuit and said second ventricular sensingcircuit, respectively, possible evoked responses during said first timewindow and said second time window, respectively, such that a suitablepulse energy for the pacing pulses delivered by said first ventricularpacing circuit and said second ventricular pacing circuit, respectively,is determined,wherein said control circuit is arranged to determine a time gapVV_(cts), that is to be used instead of VV during said capture thresholdsearch, wherein the determination of said time gap VV_(cts) involves thecalculation of a value

V1R2−ER2−Δ_(V1R2),

where V1R2 is a value which is stored in said memory and whichrepresents the time between a pacing pulse delivered by said firstventricular pacing circuit and a subsequent event sensed by said secondventricular sensing circuit during a time cycle when no pacing pulse isdelivered by said second ventricular pacing circuit, ER2 is said secondtime window and Δ_(V1R2) is a predetermined value that takes expectedvariations in V1R2 into account,and wherein VV_(cts), is determined such thatVV_(cts)≦V1R2−ER2−Δ_(V1R2) but with the additional condition thatVV_(ctS) shall not be less than 0 even if V1 R2−ER2−Δ_(V1R2) is lessthan 0.

The device is thus configured to calculate a particular time gapVV_(cts). VV_(cts) can thus be used when performing a capture thresholdsearch. If this time gap VV_(cts) is used instead of VV during thecapture threshold search, then it is avoided that an R-wave that isbeing transferred to the second ventricle from the first ventricleinterferes with the capture threshold search. Furthermore, thisparticular VV_(cts) is calculated in order to only reduce VV as much asis necessary in order to perform the capture threshold search. Thismeans that this search can be carried out in a hemodynamically optimalmanner. Moreover, it is possible to perform this capture thresholdsearch in the second ventricle even if pacing pulses are delivered bythe first ventricular pacing circuit during the same time cycle.

It can be noted that VV_(cts) is never less than 0, i.e. the order inwhich ventricular pulses are emitted by the first and second ventricularpacing circuits is not reversed.

It should be noted that configuration of a certain circuit to enablesensing and pacing of an atrium or ventricle, does not mean that thecircuit actually is connected to an atrium or a ventricle. Instead itmeans that if the heart stimulating device, in which the circuit inquestion is included, is actually implanted in a body with suitablylocated electrodes, and the circuit in question includes thoseelectrodes so as to be able to sense and pace an atrium or a ventricle.Similarly, the expressions relating to atrial or ventricular pacing andsensing circuits or the like only means that these circuits are adaptedto be able to sense typical atrial or ventricular events and that theyare able to deliver pulses which are of the kind that is typical forstimulating atria or ventricles. A “pacing pulse” or the like is thus apulse with an energy and morphology which would make it suitable to pacethe relevant heart chamber.

It should be noted that the capture threshold search can be performedeither simultaneously, i.e. during the same time cycles, for both thefirst and second ventricles or, alternatively, for one ventricle at atime.

According to one embodiment of the invention, the control circuit isconfigured such that VV_(cts) is selected as the smallest of thefollowing values:

VV and

V1R2−ER2−Δ_(V1R2),

but if V1R2−ER2−Δ_(V1R2) is less than 0, then VV_(cts) is selected to be0.

By selecting VV_(cts) in this manner, an optimal VV_(cts) for use duringthe capture threshold search is determined. VV is thus only reduced ifthis is necessary in order to avoid the above discussed problemconcerning a transferred R-wave to the second ventricle.

According to a further embodiment of the invention, the control circuitis arranged to determine a time AV_(cts), that is to be used instead ofAV during the capture threshold search, wherein the determination of thetime AV_(cts) involves the calculation of a value

AR1−ER1−Δ_(AR1),

where AR1 is a value which is stored in the memory and which representsthe time between a pacing pulse delivered by the first atrial sensingand/or pacing circuit and a subsequent event sensed by the firstventricular sensing circuit during a time cycle when no pacing pulse isdelivered by the first ventricular pacing circuit, ER1 is the first timewindow and Δ_(AR1) is a predetermined value that takes expectedvariations in AR1 into account,and wherein AV_(cts) is determined such thatAV_(cts)≦AR1−ER1−Δ_(AR1) but with the additional condition that AV_(cts)shall not be less than a predetermined minimum value for AV_(cts),wherein said minimum value is ≧0, even if AR1−ER1−Δ_(AR1) is less thanthe minimum value.

The device thus determines a value AV_(cts) that can be used instead ofAV during a capture threshold search. It is thereby avoided that anR-wave in the first ventricle, as a result of a delivered pacing pulsein the atrium, interferes with the capture threshold search.

The determination of the time AV_(cts) can also involve the calculationof a value AR2−VV_(cts)−ER2−Δ_(AR2),

where AR2 is a value which is stored in the memory and which representsthe time between a pacing pulse delivered by the first atrial sensingand/or pacing circuit and a subsequent event sensed by the secondventricular sensing circuit during a time cycle when no pacing pulse isdelivered by the second ventricular pacing circuit, VV_(cts) is aspreviously defined, ER2 is said second time window and Δ_(AR2) is apredetermined value that takes expected variations in AR2 into account,and wherein AV_(cts) is determined such thatAV_(cts)≦AR2−VV_(cts)−ER2−Δ_(AR2) but with the additional condition thatAV_(cts) shall not be less than a predetermined minimum value forAV_(cts), wherein the minimum value is ≧0, even ifAR2−VV_(cts)−ER2−Δ_(AR2) is less than the minimum value.

By using this calculation when determining AV_(cts), it is also avoidedthat an R-wave in the second ventricle, caused by a previous pacingpulse delivered by the first atrial pacing circuit, interferes with thecapture threshold search.

The AV_(cts) can be selected as the smallest of the following values:

AV,

AR1−ER1−Δ_(AR1), and

AR2−VV_(cts)−ER2−Δ_(AR2),

but with the additional condition that AV_(cts) shall not be less than apredetermined minimum value for AV_(cts) wherein the minimum value is≧0, even if AR1−ER1−Δ_(AR1) or AR2−VV_(cts)−ER2−Δ_(AR2) is less than theminimum value.

In this manner, an optimal AV_(cts) can be determined.

According to one embodiment of the invention, the minimum value forAV_(cts) can be larger than 0 but less than 90 ms, for example, largerthan 30 ms but less than 70 ms. Such minimum values for AV_(cts) havebeen found to be appropriate.

According to a further embodiment of the invention, the control circuitis configured to determine a time PV_(cts), that is to be used insteadof PV during said capture threshold search, wherein the determination ofsaid time PV_(cts) involves the calculation of a value

PR1−ER1−Δ_(PR1),

where PR1 is a value which is stored in said memory and which representsthe time between an event sensed by the first atrial sensing and/orpacing circuit and a subsequent event sensed by the first ventricularsensing circuit during a time cycle when no pacing pulse is delivered bythe first ventricular pacing circuit, ER1 is the first time window andΔ_(PR1) is a predetermined value that takes expected variations in PR1into account,and wherein PV_(cts) is determined such thatPV_(cts)≦PR1−ER1−Δ_(PR1) but with the additional condition that PV_(cts)shall not be less than a predetermined minimum value for PV_(cts),wherein the minimum value is ≧0, even if PR1−ER1−PV_(cts) is less thanthe minimum value.

In this manner, a suitable PV_(cts) can be determined to prevent anR-wave in the first ventricle, caused by a previous sensed atrial event,interferes with the capture threshold search.

Analogously to the above described embodiments in connection withAV_(cts), the determination of the time PV_(cts) can also involve thecalculation of a value PR2−VV_(cts)−ER2−Δ_(PR2),

where PR2 is a value which is stored in the memory and which representsthe time between an event sensed by the first atrial sensing and/orpacing circuit and a subsequent event sensed by the second ventricularsensing circuit during a time cycle when no pacing pulse is delivered bythe second ventricular pacing circuit, VV_(cts) is as previouslydefined, ER2 is the second time window and Δ_(PR2) is a predeterminedvalue that takes expected variations in PR2 into account,and wherein PV_(cts) is determined such thatPV_(cts)≦PR2−VV_(cts)−ER2−Δ_(PR2) but with the additional condition thatPV_(cts) shall not be less than a predetermined minimum value forPV_(cts), wherein the minimum value is ≧0, even ifPR2−VV_(cts)−ER2−Δ_(PR2) is less than the minimum value.

In this manner it is possible to determine PV_(cts) such that an R-wavein the second ventricle, caused by a previous sensed atrial event, doesnot interfere with the capture threshold search.

PV_(cts) can be selected as the smallest of the following values:

PV,

PR1−ER1−Δ_(PR1), and

PR2−VV_(cts)−ER2−Δ_(PR2),

but with the additional condition that PV_(cts) shall not be less than apredetermined minimum value for PV_(cts), wherein the minimum value is≧0, even if PR1−ER1−Δ_(PR1) or PR2−VV_(cts)−ER2−Δ_(PR2) is less than theminimum value.

In this manner an optimal PV_(cts) can be determined.

According to an embodiment of the invention, the minimum value forPV_(cts) is larger than 0 but less than 60 ms, for example larger than10 ms but less than 40 ms. Such minimum values for PV_(cts) have beenfound to be appropriate.

According to a further embodiment of the invention, the control circuitis configured to be able to carry out a search procedure for determiningV1R2, and to store the determined value of V1R2 in the memory, such thatthis stored value can be used when determining VV_(cts) in accordancewith any of the above described embodiments. According to thisembodiment, the device is thus also configured to be able to determineV1R2. The determined V1R2 can then be used when determining VV_(cts).

The control circuit can be configured such that the procedure fordetermining V1R2 also involves determining the variation in V1R2 and thedetermination of an appropriate value for Δ_(V1R2) and to store thedetermined value for Δ_(V1R2) in the memory, such that this stored valuecan be used when determining VV_(cts) in accordance with any of theabove described embodiments. The device can thus also be arranged toautomatically determine also Δ_(V1R2). This determined value can then beused when determining VV_(cts).

The control circuit can be configured such that the procedure fordetermining V1R2 includes the delivery of a pacing pulse by said firstventricular pacing circuit and the sensing of a subsequent event by thesecond ventricular sensing circuit during the same time cycle, with thecontrol circuit being configured to carry out this procedure during apart of the time cycle when no atrial events are likely to be sensed bysaid second ventricular sensing circuit. The control circuit is thus setup to determine V1R2 during a portion of the time cycle when no atrialevents are likely to cause sensing in the second ventricular sensingcircuit. This means that the control circuit ensures that the detectedR-wave actually is caused by a ventricular event in the first ventricle.

Analogously to the above determination of V1R2, the control circuit canbe configured to be able to carry out a search procedure for determiningAR1, AR2, PR1, PR2, Δ_(AR1), Δ_(AR2), Δ_(PR1) and/or Δ_(PR2) and tostore the determined values in the memory. The device is thus arrangedto be able to determine all the different values that are to be usedwhen determining VV_(cts), AV_(cts), and PV_(cts).

According to another aspect of the invention, the invention provides animplantable heart stimulating system comprising:

an implantable heart stimulating device according to any of thepreceding embodiments, andsaid first atrial sensing and/or pacing electrode,said first ventricular sensing electrode,said first ventricular pacing electrode,said second ventricular sensing electrode, andsaid second ventricular pacing electrode,wherein said electrodes are operationally connected to said device.

The system can also include a number of leads, on which the electrodesare positioned, which leads are connected to the device. The firstventricular sensing electrode can be the same as the first ventricularpacing electrode and the second ventricular sensing electrode can be thesame as the second ventricular pacing electrode.

Such a system is thus suitable to be used in a human or animal being.

Another aspect of the invention concerns a method of, in a human oranimal being, performing a capture threshold search with the help of aheart stimulating device that, during the normal operation of thedevice, is set up to operate with times VV, AV and/or PV, ER1 and ER2,where VV is the time between a pacing pulse delivered, or inhibited, toa first ventricle and a pacing pulse delivered, or inhibited, during thesame heart cycle, to a second ventricle, wherein said time gap VV is ≧0,where AV is the time between a pacing pulse to a first atrium and asubsequent pacing pulse, which may also be inhibited, to said firstventricle, where PV is the time between a sensed event in said firstatrium and a subsequent pacing pulse, which may also be inhibited, tosaid first ventricle, where ER1 is the evoked response detection windowfor the first ventricle and where ER2 is the evoked response detectionwindow for the second ventricle. The method includes the followingsteps:

determine a value V1R2, where V1R2 represents the time between a pacingpulse to the first ventricule and a subsequent event in the secondventricle, during a heart cycle when no pacing pulse is delivered to thesecond ventricle;determine Δ_(V1R2), where Δ_(V1R2) is a value that takes expectedvariations in V1R2 into account;determine a time gap VV_(cts) that is to be used instead of VV duringsaid capture threshold search, such thatVV_(cts)≦V1R2−ER2−Δ_(V1R2) but with the additional condition thatVV_(cts) shall not be less than 0 even if V1R2−ER2−Δ_(V1R2) is less than0; andperform a capture threshold search by using VV_(cts) instead of VV.

The method can involve the selection of VV_(cts) as the smallest of thefollowing values: VV and

V1R2−ER2−Δ_(V1R2),

but if V1R2−ER2−Δ_(V1R2) is less than 0, then VV_(cts) is selected to be0.

With such a method, advantages corresponding to those described above inconnection with the device are obtained.

The method can also involve the determination of AR1, AR2, PR1, PR2,Δ_(AR1), Δ_(AR2), Δ_(PR1), and/or Δ_(PR2) and to use the determinedvalues when determining AV_(cts) and PV_(cts) and, furthermore, toperform a capture threshold search by using AV_(cts) and PV_(cts)instead of AV and PV.

By actually using the determined values for VV_(cts), AV_(cts), andPV_(cts) during a capture threshold search, this search can be performedin an hemodynamically optimal manner.

The method can be performed on a human or animal being suffering fromcongestive heart failure, for example on a on a human or animal beingsuffering from a bundle branch block.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically a heart stimulating system with a heartstimulating device connected to leads with sensing and pacing electrodespositioned in a heart.

FIG. 2 shows schematically a control circuit which may form part of thedevice.

FIG. 3 shows schematically a somewhat more detailed illustration of partof the control circuit of FIG. 2.

FIG. 4 illustrates schematically a method according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows schematically an implantable heart stimulating device 10according to the invention. The device 10 comprises a housing 12. Thehousing 12 includes a control circuit 14. The device 10 comprises aconnector portion 13. Via the connector portion 13, the device 10 can beconnected to different leads. In FIG. 1 the device 10 is connected tothree leads 20, 30 and 40.

The lead 20 includes a pacing and sensing electrode 21, 22. In the shownexample, this electrode 21, 22 is a bipolar electrode with a tip portion21 and a ring portion 22. However, it is within of the scope of theinvention that instead unipolar electrodes can be used, as is known to aperson skilled in the art. Similarly to the lead 20, the lead 30includes a pacing and sensing electrode 31, 32 and the lead 40 includesa pacing and sensing electrode 41, 42. The device 10 together with theleads 20, 30, 40 and the electrodes 21, 22; 31, 32; 41 42 constitutes anembodiment of an implantable heart stimulating system according to theinvention.

FIG. 1 also schematically illustrates a heart with a right atrium RA, aleft atrium LA, a right ventricle RV and a left ventricle LV.

The electrode 21, 22 constitutes a first atrial sensing and/or pacingelectrode 21, 22 which is positioned in a first atrium 1A of the heart,according to this embodiment the right atrium RA, in order to enablesensing and/or pacing of this atrium RA.

The electrode 31, 32 constitutes a first ventricular sensing and pacingelectrode 31, 32, which is positioned in a first ventricle 1V of theheart, in this embodiment the right ventricle RV. The first ventricularsensing and pacing electrode 31, 32 is adapted to enable sensing andpacing of this first ventricle 1V.

The electrode 41, 42 constitutes a second ventricular sensing and pacingelectrode 41, 42, which is positioned at a second ventricle 2V of theheart, in this embodiment the left ventricle LV. The second ventricularsensing and pacing electrode 41, 42 is adapted to enable sensing andpacing of this second ventricle 2V. The lead 40 may for example beintroduced via the right atrium RA and the coronary sinus such that theelectrode 41, 42 is positioned in for example the middle or greatcardiac vein of the heart. How to introduce the lead 40 in this manneris known to a person skilled in the art.

Although not shown in FIG. 1, it is also possible that the system isconnected to further leads and/or further electrodes, for exampleelectrodes positioned in order to sense and/or pace the left atrium LAand electrodes designed to enable defibrillation.

FIG. 2 shows schematically the control circuit 14 in some more detail.The control circuit 14 includes a memory 15 connected to a controlportion 18. The control circuit 14 includes a first atrial sensingand/or pacing circuit 25, 27. In this embodiment, this circuit 25, 27includes a sensing circuit 25 and a pacing circuit 27. The first atrialsensing and/or pacing circuit 25, 27 communicates with the first atrialsensing and/or pacing electrode 21, 22 via the lead 20. The first atrialsensing and/or pacing circuit 25, 27 is thus adapted to sense and/orpace an atrium 1A, in this case the right atrium RA.

The control circuit 14 also includes a first ventricular sensing circuit35 and a first ventricular pacing circuit 37. These circuits 35, 37communicate with the first ventricular sensing and pacing electrode 31,32 via the lead 30. The circuits 35, 37 are thus adapted to sense andpace a first ventricle 1V, in this case the right ventricle RV.

The control circuit 14 also includes a second ventricular sensingcircuit 45 and a second ventricular pacing circuit 47. These circuits45, 47 communicate with the second ventricular sensing and pacingelectrode 41, 42 via the lead 40. These circuits 45, 47 are adapted tosense and pace a second ventricle 2V, in this case the left ventricleLV.

The control circuit 14 is configured, or programmed, to include severaloperational features. The control circuit is thus arranged to be able todetect an evoked response to a pacing pulse delivered by said firstventricular pacing circuit 37 by sensing, with said first ventricularsensing circuit 35, within a first time window ER1 that follows after apacing pulse delivered by said first ventricular pacing circuit 37.

Similarly, the control circuit 14 is also configured to be able todetect an evoked response to a pacing pulse delivered by said secondventricular pacing circuit 47 by sensing, with said second ventricularsensing circuit 45, within a second time window ER2 that follows after apacing pulse delivered by said second ventricular pacing circuit 47.

The basic design for a pacer to sense evoked response is known to thoseskilled in the art. The first time window ER1 may for example be set tobegin 5 ms to 30 ms, for example 15 ms, after the delivery of a pacingpulse by the first ventricular pacing circuit 37. The length of thefirst time window ER1 may for example be 30 ms to 70 ms, for example 50ms. Analogously, the second time window ER2 can for example be set tobegin 5 ms to 30 ms, for example 15 ms, after the delivery of a pacingpulse by the second ventricular pacing circuit 47. The length of thesecond time window ER2 may for example be 30 ms to 70 ms, for example 50ms. It should be noted that the first ER1 and second ER2 time windows donot necessarily have to have the same length and they do not necessarilyhave to start or end the same the time period after the respectivedelivered pacing pulse.

As is normal in a heart stimulating device, the first ventricularsensing circuit 35 and the second ventricular sensing circuit 45 arealso able to sense events typical for an R-wave (QRS-complex) in therespective ventricle.

FIG. 3 shows schematically a part of the control circuit 14 in some moredetail. FIG. 3 illustrates that the first ventricular sensing circuit 35is connected to an evoked response detection logic 50 and an R-wavedetection logic 51. The detection logics 50 and 51 can be seen to formpart of the control portion 18 illustrated in FIG. 2. Preferably,similar detection logics are of course arranged also for the secondventricular sensing circuit 45. The detection logic 50 is thus optimizedto sense an evoked response and the detection logic 51 is optimized todetect an R-wave.

As is also normal in a heart stimulating device, the first atrialsensing and/or pacing circuit 25, 27 is also arranged to be able todetect events typical for a P-wave.

The control circuit 14 is arranged to be able to operate with timecycles corresponding to normal heart cycles. Such an operation is normalfor an implantable heart stimulating device. The time cycles aredetermined by preset timer intervals which also may depend on detectedsignals

The control circuit 14 is also arranged to be able to operate, duringthe normal operation of the device 10, with a value PV and/or AV. PV isthe time between the sensing with the first atrial sensing and/or pacingcircuit 25, 27 and a subsequent pacing pulse, which may also beinhibited, of the first ventricular pacing circuit 37. AV is the timebetween the pacing with said first atrial sensing and/or pacing circuit25, 27 and a subsequent pacing pulse, which may also be inhibited, ofsaid first ventricular pacing circuit 37. It is well known to thoseskilled in the art how an implantable heart stimulating device is set upin order to operate with PV and AV intervals. It is also known that thedelivery of pacing pulses can be inhibited.

The control circuit 14 is also configured to be able to deliver, withina time cycle, pacing pulse with both said first ventricular pacingcircuit 37 and said second ventricular pacing circuit 47 with a time gapVV, during the normal operation of the device 10, between a pacing pulsedelivered, or inhibited, by the first ventricular pacing circuit 37 anda pacing pulse delivered, or inhibited, by the second ventricular pacingcircuit 47, wherein the time gap VV is ≧0. A typical value of VV can bebetween 0 ms and 80 ms.

In the present case, the AV and PV intervals are thus defined inrelation to the ventricular pacing circuit that is paced (or inhibited)first (if VV is not equal to 0; if VV is 0 then, of course, the firstand second ventricular pacing circuits operate simultaneously). Withthis definition, VV cannot be less than 0. The ventrical that isreferred to as the first ventricle 1V is thus, in the presentembodiment, the ventricle that is paced (or inhibited) first, if VV isnot equal to 0. This ventricle can be either the left LV or the right RVventricle depending on the particular case. However, the presentinvention is intended to extend also to the situation where some otherdefinition of the PV and AV intervals is used, e.g. if VV can benegative.

The control circuit 14 is also arranged to be able to carry out acapture threshold search, by during a number of time cycles, vary theenergy of the pacing pulses delivered by the first ventricular pacingcircuit 37 and the second ventricular pacing circuit 47 and to detect,with the first ventricular sensing circuit 35 and the second ventricularsensing circuit 45, respectively, possible evoked responses during thefirst time window ER1 and the second time window ER2, respectively, suchthat a suitable pulse energy for the pacing pulses delivered by thefirst ventricular pacing circuit 37 and the second ventricular pacingcircuit 47, respectively, is determined. The suitable pulse energy canbe selected somewhat higher than the actually measured threshold, inorder to have a safety margin. According to the present invention, thecapture threshold search can either be carried simultaneously (duringthe same time cycles) for both the first and second channels, or,alternatively, in one channel at a time. The device 10 can be configuredto perform a capture, threshold search periodically, for example once aday, but it is also possible that the device 10 is set up to performsuch a search when a predetermined number of lack of capture beats havebeen detected.

As has been explained above, it may be necessary to reduce the differenttimes AV, PV during a capture threshold search in order to avoid fusion.According to the present invention this is done in an optimal manner.Furthermore, according to the present invention, also VV is reduced, ifnecessary, in an optimal manner when a capture threshold search is beingcarried out.

When a capture threshold search is to be carried out, first someintrinsic conduction times have to be determined and stored in thememory. This can be done just before the capture threshold search iscarried out. However, it is also possible to determine the intrinsicconduction times at an earlier stage.

First some abbreviations that are used below will be explained.

V1R2 is a value which represents the time between a pacing pulsedelivered by said first ventricular pacing circuit 37 and a subsequentevent sensed by said second ventricular sensing circuit 45 during a timecycle when no pacing pulse is delivered by said second ventricularpacing circuit 47. This time thus represents the time it takes for apaced R-wave in the first ventricle 1V to be transferred to the secondventricle 2V.

Δ_(V1R2) is a value that takes expected variations in V1R2 into account.

AR1 is a value which represents the time between a pacing pulsedelivered by said first atrial sensing and/or pacing circuit 25, 27 anda subsequent event sensed by the first ventricular sensing circuit 35during a time cycle when no pacing pulse is delivered by said firstventricular pacing circuit 37. AR1 thus represents the conduction timefrom a paced event in the atrium 1A to a detected R-wave in the firstventricle 1V.

Δ_(AR1), is a predetermined value that takes expected variations in AR1into account.

AR2 is a value which represents the time between a pacing pulsedelivered by the first atrial sensing and/or pacing circuit 25, 27 and asubsequent event sensed by the second ventricular sensing circuit 45during a time cycle when no pacing pulse is delivered by said secondventricular pacing circuit 47. AR2 thus represents the conduction timefrom a paced event in the atrium 1A to a detected R-wave in the secondventricle 2V.

Δ_(AR2) is a predetermined value that takes expected variations in AR2into account.

PR1 is a value which represents the time between an event sensed by thefirst atrial sensing and/or pacing circuit 25, 27 and a subsequent eventsensed by the first ventricular sensing circuit 35 during a time cyclewhen no pacing pulse is delivered by the first ventricular pacingcircuit 37. PR1 thus represents the conduction time from a sensed eventin the atrium 1A to a detected R-wave in the first ventricle 1V.

Δ_(PR1) is a predetermined value that takes expected variations in PR1into account.

PR2 is a value which represents the time between an event sensed by thefirst atrial sensing and/or pacing circuit 25, 27 and a subsequent eventsensed by the second ventricular sensing circuit 45 during a time cyclewhen no pacing pulse is delivered by the second ventricular pacingcircuit 47. PR2 thus represents the conduction time from a sensed eventin the atrium 1A to a detected R-wave in the second ventricle 2V,

Δ_(PR2) is a predetermined value that takes expected variations in PR2into account.

The device 10 is thus configured to determine intrinsic conductiontimes.

The control circuit 14 is arranged to carry out a search procedure fordetermining V1R2, and to store the determined value of V1R2 in thememory 15. This procedure includes the delivery of a pacing pulse withthe first ventricular pacing circuit 37 and the sensing of a subsequentevent by the second ventricular sensing circuit 45 during the same timecycle. The control circuit 14 is arranged to carry out this procedureduring a part of the time cycle when no atrial events are likely to besensed by the second ventricular sensing circuit 45, i.e. the part ofthe time cycle when no sensing in the second ventricle 2V caused by aprevious atrial event is likely to occur. This procedure also involvesdetermining the variation in V1R2 and the determination of anappropriate value for Δ_(V1R2) and to store the determined value forΔ_(V1R2) in the memory 15. The determined value of Δ_(V1R2) thus canrepresent, for example, the mean value of the conduction times V1R2measured during a number of heart cycles, for example 10 heart cycles.Δ_(V1R2) can be determined statistically and can thus represent somemeasure of the variation in V1R2. For example, Δ_(V1R2) can be selectedsuch that an expected value of V1R2 with a certain probability, forexample 98% percent probability, will fall within the rangeV1R2±Δ_(V1R2).

Analogously, the control circuit 14 is arranged to carry out a searchprocedure for determining AR1, and to store the determined value of AR1in the memory 15. The procedure for determining AR1 includes thedelivery of a pacing pulse with the first atrial sensing and/or pacingcircuit 25, 27 and the sensing of a subsequent event with the firstventricular sensing circuit 35 during the same time cycle. The controlcircuit 14 is arranged such that no pacing pulse is delivered by thefirst ventricular pacing circuit 37 during this time cycle. Theprocedure for determining AR1 also involves determining the variation inAR1 and the determination of an appropriate value for Δ_(AR1) and tostore the determined value for Δ_(AR1) in the memory 15.

Analogously, the control circuit 14 is arranged to carry out a searchprocedure for determining AR2, and to store the determined value of AR2in the memory 15. The procedure for determining AR2 includes thedelivery of a pacing pulse with the first atrial sensing and/or pacingcircuit 25, 27 and the sensing of a subsequent event with the secondventricular sensing circuit 45 during the same time cycle. The controlcircuit 14 is arranged such that no pacing pulse is delivered by thesecond ventricular pacing circuit 47 during this time cycle. Thisprocedure also involves determining the variation in AR2 and thedetermination of an appropriate value for Δ_(AR2) and to store thedetermined value for Δ_(AR2) in the memory 15,

Analogously, the control circuit 14 is arranged to carry out a searchprocedure for determining PR1, and to store the determined value of PR1in the memory 15. This procedure includes the sensing with the firstatrial sensing and/or pacing circuit 25, 27 and the sensing of asubsequent event with the first ventricular sensing circuit 35 duringthe same time cycle. No pacing pulse is delivered by the firstventricular pacing circuit 37 during this time cycle. The procedure fordetermining PR1 also involves determining the variation in PR1 and thedetermination of an appropriate value for Δ_(PR1) and to store thedetermined value for Δ_(PR1) in the memory 15.

The control circuit 14 is also arranged to carry out a search procedurefor determining PR2, and to store the determined value of PR2 in thememory 15. This procedure includes the sensing with the first atrialsensing and/or pacing circuit 25, 27 and the sensing of a subsequentevent with the second ventricular sensing circuit 45 during the sametime cycle. The control circuit 14 is arranged such that no pacing pulseis delivered by the second ventricular pacing circuit 47 during thistime cycle. This procedure also involves determining the variation inPR2 and the determination of an appropriate value for Δ_(PR2) and tostore the determined value for Δ_(PR2) in the memory 15.

AR1, AR2, PR1 and PR2 can be determined as a mean or average valuesimilarly to the determination of V1R2 described above. Also theprocedures for determining Δ_(AR1), Δ_(AR2), Δ_(PR1) and Δ_(PR2) can beperformed in a similar manner to that described above in connection withthe determination of Δ_(V1R2).

As noted above, no pacing pulse is delivered by certain pacing circuitsduring the time cycles when the different intrinsic conduction times aredetermined. It is of course also possible to deliver a pacing pulseduring the same time cycle if such a pacing pulse is delivered during apart of the time cycle when it will not interfere with the detection ofthe intrinsic conduction. This can be, for example, achieved if certainpacing intervals, such as AV or PV, are increased during suchdetermination of intrinsic conduction times.

Furthermore, the control circuit 14 is configured to determine a timegap VV_(cts), that is to be used instead of VV during the capturethreshold search. VV_(cts) is hereby selected as the smallest of thefollowing values;

VV and

V1R2−ER2−Δ_(V1R2),

but if V1R2−ER2−, Δ_(V1R2) is less than 0, then VV_(cts) is selected tobe 0.

Furthermore, the control circuit 14 is arranged to determine a timeAV_(cts), that is to be used instead of AV during the capture thresholdsearch. AV_(cts) is selected as the smallest of the following values:

AV,

AR1−ER1−Δ_(AR1), and

AR2−VV_(cts)−ER2−Δ_(AR2)

but with the additional condition that AV_(cts) shall not be less than apredetermined minimum value for AV_(cts), wherein the minimum value is≧0, even if AR1−ER1−Δ_(AR1) or AR2−VV_(cts)−ER2−Δ_(AR2) is less than theminimum value. The minimum value for AV_(cts) can for example be 50 ms.

Moreover, the control circuit 14 is configured to determine a timePV_(cts), that is to be used instead of PV during the capture thresholdsearch. PV_(cts) is selected as the smallest of the following values:

PV,

PR1−ER1−Δ_(PR1), and

PR2−VV_(cts),−ER2−Δ_(PR2),

but with the additional condition that PV_(cts) shall not be less than apredetermined minimum value for PV_(cts), wherein the minimum value is≧0, even if PR1−ER1−Δ_(PR1) Or PR2−VV_(cts)−ER2−Δ_(PR2) is less than theminimum value. The minimum value for PV_(cts) can for example be 25 ms.

Finally, the control circuit 14 is configured to be able to use thedetermined values for VV_(cts), AV_(cts) and PV_(cts), instead of VV, AVand PV when actually performing a capture threshold search.

The invention also provides a method of, in a human or animal being,performing a capture threshold search with the help of a heartstimulating device.

FIG. 4 discloses very schematically a flow chart for such a method. Atthe same time, this figure illustrates schematically how a device 10according to the invention can operate.

The device normally operates with times VV, AV and/or PV, ER1 and ER2 asexplained above.

A capture threshold search can be performed at regular intervals, forexample once a day, or when a certain number of loss of capture has beendetected.

If a capture threshold search is to be carried out, then first thevalues for V1R2, AR1, AR2, PR1, PR2, Δ_(V1R2), Δ_(AR1), Δ_(AR2), Δ_(PR1)and Δ_(PR2) are determined. These values can for example be determinedas explained above or in any other suitable manner. For example, if anyof these values is known before with sufficient accuracy, then it maynot be necessary to perform a special search for finding out this value.Moreover, these values can either be determined just before the capturethreshold search is performed, or these values can have been determinedearlier.

Thereafter a the times VV_(cts), AV_(cts), and PV_(cts), that that areto be used instead of VV, AV and PV, respectively, during said capturethreshold search are determined. These times can be determined asfollows.

VV_(cts) is selected as the smallest of the following values:

VV and

V1R2−ER2−Δ_(V1R2),

but if V1R2−ER2−Δ_(V1R2) is less than 0, then VV_(cts) is selected to be0.

AV_(cts) is selected as the smallest of the following values:

AV,

AR1−ER1−Δ_(AR1), and

AR2−VV_(cts)−ER2−Δ_(AR2),

but with the additional condition that AV_(cts) shall not be less than apredetermined minimum value for AV_(cts), for example 50 ms, even ifAR1−ER1−Δ_(AR1), or AR2−VV_(cts), −ER2−Δ_(AR2) is less than 50 ms.

PV_(cts) is selected as the smallest of the following values:

PV,

PRI−ER1−Δ_(PR1), and

PR2−VV_(cts)−ER2−Δ_(PR2),

but with the additional condition that PV_(cts) shall not be less than apredetermined minimum value for PV_(cts), for example 25 ms, even ifPR1−ER1−Δ_(PR1) or PR2−VV_(cts)−ER2−Δ_(PR2) is less than 25 ms.

The method then also includes the step of actually performing a capturethreshold search by using VV_(cts), AV_(cts) and PV_(cts) instead of W,AV and PV. Based on the capture threshold search, a suitable stimulationamplitude can be selected. The stimulation amplitude is set such that acertain safety margin is achieved How to select a certain safety marginis known from prior devices that operate with an evoked responsedetection.

The method can be performed on a human or animal being suffering fromcongestive heart failure, for example on a on a human or animal beingsuffering from a bundle branch block.

It should be noted that it is of course only necessary to determine anduse those values which are essential for the operation in the particularcase. For example, if sensing in the atrium is not used, then it is ofcourse not necessary to determine PV_(cts) or the values needed fordetermining PV_(cts).

Although modifications and changes may be suggested by those skilled inthe art, it is the intention of the inventors to embody within thepatent warranted heron all changes and modifications as reasonably andproperly come within the scope of their contribution to the art.

1. An implantable heart stimulating device comprising: at least onememory; a first atrial sensing and/or pacing circuit configured tocommunicate with a first atrial sensing and/or pacing electrodeconfigured to be positioned in an atrium of a heart, said first atrialsensing and/or pacing circuit being configured to enable sensing and/orpacing of the atrium; a first ventricular sensing circuit configured, tocommunicate with a first ventricular sensing electrode configured to bepositioned in or at a first ventricle of said heart, said firstventricular sensing circuit being configured to enable sensing of thefirst ventricle; a first ventricular pacing circuit configured tocommunicate with a first ventricular pacing electrode configured to bepositioned in or at the first ventricle of said heart, said firstventricular pacing circuit being configured to enable pacing of thefirst ventricle; a second ventricular sensing circuit configured tocommunicate with a second ventricular sensing electrode configured to bepositioned in or at a second ventricle of said heart, said secondventricular sensing circuit being configured to enable sensing of thesecond ventricle; a second ventricular pacing circuit configured tocommunicate with a second ventricular pacing electrode configured to bepositioned in or at the second ventricle of said heart, said secondventricular pacing circuit being configured to enable pacing of thesecond ventricle; a control circuit configured to detect an evokedresponse to a pacing pulse delivered by said first ventricular pacingcircuit by sensing, with said first ventricular sensing circuit, withina first time window that follows after a pacing pulse delivered by saidfirst ventricular pacing circuit; a control circuit being configured todetect an evoked response to a pacing pulse delivered by said secondventricular pacing circuit by sensing, with said second ventricularsensing circuit within a second time window that follows after a pacingpulse delivered by said second ventricular pacing circuit; said controlcircuit being configured to operate with time cycles corresponding tonormal heart cycles; said control circuit being configured to operate,during the normal operation of the device, with a value PV and/or AV,where PV is the time between the sensing with said first atrial sensingand/or pacing circuit and a subsequent pacing pulse, which may also beinhibited, of said first ventricular pacing circuit and AV is the timebetween the pacing with said first atrial sensing and/or pacing circuitand a subsequent pacing pulse, which may also be inhibited, of saidfirst ventricular pacing circuit; said control circuit being configuredto deliver, within a time cycle pacing pulse with both said firstventricular pacing circuit and said second ventricular pacing circuitwith a time gap VV, during the normal operation of the device, between apacing pulse delivered, or inhibited, by said first ventricular pacingcircuit and a pacing pulse delivered, or inhibited, by said secondventricular pacing circuit, wherein said time gap VV is ≧0; said controlcircuit being configured to execute a capture threshold search, by,during a plurality of time cycles, vary the energy of the pacing pulsesdelivered by said first ventricular pacing circuit and said secondventricular pacing circuit and to detect, with said first ventricularsensing circuit and said second ventricular sensing circuit,respectively, possible evoked responses during said first time windowand said second time window, respectively, and to determine a suitablepulse energy for the pacing pulses delivered by said first ventricularpacing circuit and said second ventricular pacing circuit, respectively;said control circuit being configured to determine a time gap VV_(cts)that is to be used instead of VV during said capture threshold search,by calculating a value V1R2−ER2−Δ_(V1R2), where V1R2 is a value which isstored in said memory and which represents the time between a pacingpulse delivered by said first ventricular pacing circuit and asubsequent event sensed by said second ventricular sensing circuitduring a time cycle when no pacing pulse is delivered by said secondventricular pacing circuit, ER2 is said second time windows, andΔ_(V1R2) is a predetermined value that takes expected variations in V1R2into account, and by setting VV_(cts) such thatVV_(cts)<V1R2−ER2−Δ_(V1R2) but with the additional condition thatVV_(cts) shall not be less than 0 even if V1R2−ER2−Δ_(V1R2) is less than0.
 2. An implantable heart stimulating device according to claim 1,wherein the control circuit is configured to set VV_(cts) as thesmallest of the following values:VV andV1R2−ER2−Δ_(V1R1), but if V1R2−ER2−Δ_(V1R2) is less than 0, thenVV_(cts) is selected to be
 0. 3. An implantable heart stimulating deviceaccording to claim 1, wherein the control circuit is configured todetermine a time AV_(cts), that is to be used instead of AV during saidcapture threshold search, by calculating a valueAR1−ER1−Δ_(AR1), where AR1 is a value which is stored in said memory andwhich represents the time between a pacing pulse delivered by said firstatrial sensing and/or pacing circuit (25, 27) and a subsequent eventsensed by said first ventricular sensing circuit (35) during a timecycle when no pacing pulse is delivered by said first ventricular pacingcircuit (37), ER1 is said first time window and Δ_(AR1) is apredetermined value that takes expected variations in AR1 into account,and wherein AV_(cts) is set such that AV_(cts)≦AR1−ER1−Δ_(AR1) but withthe additional condition that AV_(cts) shall not be less than apredetermined minimum value for AV_(cts), wherein said minimum value is≧0, even if AR1−ER1−Δ_(AR1) is less than said minimum value.
 4. Animplantable heart stimulating device according to claim 3, wherein thedetermination of said time AV_(cts) also involves the calculation of avalueAR2−VV_(cts)−ER2−Δ_(AR2), where AR2 is a value which is stored in saidmemory and which represents the time between a pacing pulse delivered bysaid first atrial sensing and/or pacing circuit and a subsequent eventsensed by said second ventricular sensing circuit during a time cyclewhen no pacing pulse is delivered by said second ventricular pacingcircuit, VV_(cts) is as previously defined, ER2 is said second timewindow and Δ_(AR2) is a predetermined value that takes expectedvariations in AR2 into account, and wherein said control circuit setsAV_(cts) such that AV_(cts)≦AR2−VV_(cts)−ER2−Δ_(AR2) but with theadditional condition that AV_(cts) shall not be less than apredetermined minimum value for AV_(cts), wherein said minimum value is≧0, even if AR2−VV_(cts)−ER2−Δ_(AR2) is less than said minimum value. 5.An implantable heart stimulating device according to claim 4, whereinthe control circuit is configured to set AV_(cts) as the smallest of thefollowing values:AV,AR1−ER1−Δ_(AR1), andAR2−VV_(cts)−ER2−Δ_(AR2), but with the additional condition thatAV_(cts) shall not be less than a predetermined minimum value forAV_(cts), wherein said minimum value is ≧0 even if AR1−ER1−Δ_(AR1) orAR2−VV_(cts)−ER2−Δ_(AR2) is less than said minimum value.
 6. Animplantable heart stimulating device according to claim 3, wherein thecircuit employs a minimum value for AV_(cts) that is larger than 0 butless than 90 ms.
 7. An implantable heart stimulating device according toclaim 6, wherein the control circuit employs a minimum value forAV_(cts), that is larger than 30 ms but less than 70 ms.
 8. Animplantable heart stimulating device according to claim 1, wherein thecontrol circuit is configured to determine a time PV_(cts), that is tobe used instead of PV during said capture threshold search, controlcircuit determining said time PV_(cts) calculating a valuePR1−ER1−Δ_(PR1), where PR1 is a value which is stored in said memory andwhich represents the time between an event sensed by said first atrialsensing and/or pacing circuit and a subsequent event sensed by saidfirst ventricular sensing circuit during a time cycle when no pacingpulse is delivered by said first ventricular pacing circuit, ER1 is saidfirst time window and Δ_(PR1) is a predetermined value that takesexpected variations in PR1 into account, and wherein the control circuitsets PV_(cts) such that PV_(cts)≦PR1−ER1−Δ_(PR1) but with the additionalcondition that PV_(cts) shall not be less than a predetermined minimumvalue for PV_(cts), wherein said minimum value is ≧0, even ifPR1−ER1−Δ_(PR1) is less than said minimum value.
 9. An implantable heartstimulating device according to claim 8, wherein the control circuitdetermines of said time PV_(cts) by also calculating a valuePR2−VV_(cts)−ER2−Δ_(PR2), where PR2 is a value which is stored in saidmemory and which represents the time between an event sensed by saidfirst atrial sensing and/or pacing circuit and a subsequent event sensedby said second ventricular sensing circuit during a time cycle when nopacing pulse is delivered by said second ventricular pacing circuit,VV_(cts) is as previously defined, ER2 is said second time window andΔ_(PR2) is a predetermined value that takes expected variations in PR2into account, and wherein PV_(cts) is determined such thatPV_(cts)≦PR2−VV_(cts)−ER2−Δ_(PR2) but with the additional condition thatPV_(cts) shall not be less than a predetermined minimum value forPV_(cts), wherein said minimum value is ≧0, even ifPR2−VV_(cts)−ER2−Δ_(PR2) is less than said minimum value.
 10. Animplantable heart stimulating device according to claim 9, wherein thecontrol circuit is configured to set PV_(cts) as the smallest of thefollowing values:PV,PR1−ER1−Δ_(PR1), andPR2−VV_(cts)−ER2−Δ_(PR2), but with the additional condition thatPV_(cts) shall not be less than a predetermined minimum value forPV_(cts), wherein said minimum value is ≧0, even if PR1−ER1−Δ_(PR1) orPR2−VV_(cts), −ER2−Δ_(PR2) is less than said minimum value.
 11. Animplantable heart stimulating device according to claim 8, wherein thecontrol circuit employs a minimum value for PV_(cts) that is larger than0 but less than 60 ms.
 12. An implantable heart stimulating deviceaccording to claim 11, wherein the control circuit employs a minimumvalue for PV_(cts), that is larger than 10 ms but less than 40 ms. 13.An implantable heart stimulating device according to claim 1, whereinthe control circuit is configured to execute a search procedure fordetermining V1R2, and to store a value of V1R2 determined in said searchprocedure in said memory use when determining VV_(cts).
 14. Animplantable heart stimulating device according to claim 13, wherein thecontrol circuit is configured in the procedure for determining V1R2, toalso determine a variation in V1R2 and to determine a value for Δ_(V1R2)and to store the determined value for Δ_(V1R2) in said memory, for usewhen determining VV_(cts).
 15. An implantable heart stimulating deviceaccording to claim 13, wherein the control circuit is configured toexecute the procedure for determining by causing delivery of a pacingpulse by said first ventricular pacing circuit and the sensing of asubsequent event by said second ventricular sensing circuit during thesame time cycle, and wherein the control circuit is configured toexecute said procedure during a part of the time cycle when no atrialevents are likely to be sensed by said second ventricular sensingcircuit.
 16. An implantable heart stimulating device according to claim3, wherein the control circuit is configured to execute a searchprocedure for determining AR1, and to store a value determined in saidsearch procedure of AR1 in said memory, for use when determiningAV_(cts).
 17. An implantable heart stimulating device according to claim16, wherein the control circuit is configured in the procedure fordetermining AR1, to also determine a variation in AR1 and to determine avalue for Δ_(AR1) and to store the determined value for Δ_(AR1), in saidmemory, for use when determining AV_(cts).
 18. An implantable heartstimulating device according to claim 16, wherein the control circuit isto execute the procedure for determining AR1 by causing delivery of apacing pulse by said a first atrial sensing and/or pacing circuit andthe sensing of a subsequent event by said first ventricular sensingcircuit during the same time cycle, and the control circuit isconfigured to cause no pacing pulse to be delivered by said firstventricular pacing circuit during this time cycle.
 19. An implantableheart stimulating device according to claim 4, wherein the controlcircuit is configured to execute a search procedure for determining AR2,and to store the determined value of AR2 in said memory, for use whendetermining AV_(cts).
 20. An implantable heart stimulating deviceaccording to claim 19, wherein the control circuit is configured, in theprocedure for determining AR2, to also determine a variation in AR2 andto determine a value for Δ_(AR2) and to store the value for Δ_(AR2)determined in said procedure in said memory, for use when determiningAV_(cts).
 21. An implantable heart stimulating device according to claim19, wherein the control circuit is configured in the procedure fordetermining AR2, to cause delivery of a pacing pulse by said firstatrial sensing and/or pacing circuit and the sensing of a subsequentevent by said second ventricular sensing circuit during the same timecycle, and wherein the control circuit is configured to cause no pacingpulse to be delivered by said second ventricular pacing circuit duringthis time cycle.
 22. An implantable heart stimulating device accordingto claim 8, wherein the control circuit is configured to execute asearch procedure for determining PR1, and to store a value of PR1determined in said search procedure in said memory for use whendetermining PV_(cts).
 23. An implantable heart stimulating deviceaccording to claim 22, wherein the control circuit is configured in theprocedure for determining PR1 to also determine variation in PR1 and todetermine a value for Δ_(PR1) and to store the determined value forΔ_(PR1) in said memory for use when determining PV_(cts).
 24. Animplantable heart stimulating device according to claim 22, wherein thecontrol circuit is configured in the procedure for determining PR1, tosense with said first atrial sensing and/or pacing circuit and to sensea subsequent event by said first ventricular sensing circuit during thesame time cycle, and wherein the control circuit is configured to causeno pacing pulse to be delivered by said first ventricular pacing circuitduring this time cycle.
 25. An implantable heart stimulating deviceaccording to claim 9, wherein the control circuit is configured toexecute a search procedure for determining PR2, and to store a value ofPR2 determined in search procedures in said memory for use whendetermining PV_(cts).
 26. An implantable heart stimulating deviceaccording to claim 25, wherein the control circuit is such configured inthe procedure for determining PR2, to also determine a variation in PR2and to determine a value for Δ_(PR2) and to store the determined valuefor Δ_(PR2) in said memory for use when determining PV_(cts).
 27. Animplantable heart stimulating device according to claim 25, wherein thecontrol circuit is configured in the procedure for determining PR2, tosense with said first atrial sensing and/or pacing circuit and to sensea subsequent event by said second ventricular sensing circuit during thesame time cycle, and wherein the control circuit is configured to causeno pacing pulse to be delivered by said second ventricular pacingcircuit during this time cycle. 28-30. (canceled)
 31. A method of, in ahuman or animal being, performing a capture threshold search using aheart stimulating device that, during normal operation of the device, isset to operate with times VV, AV and/or PV, ER1 and ER2, where VV is atime between a pacing pulse delivered, or inhibited, to a firstventricle and a pacing pulse delivered, or inhibited, during the sameheart cycle, to a second ventricle, wherein said time gap VV is ≧0,where AV is a time between a pacing pulse to a first atrium and asubsequent pacing pulse, which may also be inhibited, to said firstventricle, where PV is a time between a sensed event in said firstatrium and a subsequent pacing pulse, which may also be inhibited, tosaid first ventricle, where ER1 is an evoked response detection windowfor the first ventricle and where ER2 is an evoked response detectionwindow for the second ventricle, said method comprising the steps of:automatically determining a value V1R2, where V1R2 represents a timebetween a pacing pulse to the first ventricle and a subsequent event inthe second ventricle, during a heart cycle when no pacing pulse isdelivered to the second ventricle; automatically determining Δ_(V1R2),where Δ_(V1R2) is a value that takes expected variations in V1R2 intoaccount; determine automatically determining a time gap VV_(cts), thatis to be used instead of VV during said capture threshold search, Ohthat with VV_(cts)≦V1R2−ER2−Δ_(V1R2) but with the additional conditionthat VV_(cts) shall not be less than 0 even if V1R2−ER2−Δ_(V1R2) is lessthan 0; and perform a capture threshold search by using VV_(cts),instead of VV.
 32. A method according to claim 31, comprising settingVV_(cts) as the smallest of the following values:VV andV1R2−ER2−Δ_(V1R2), but if V1R2−ER2−Δ_(V1R2) is less than 0, thenVV_(cts) is selected to be
 0. 33. A method according to claim 31comprising: determine automatically determining a value AR1, where AR1represents a time between a pacing pulse to the first atrium and asubsequent event in the first ventricle, during a heart cycle when nopacing pulse is delivered to the first ventricle; automaticallydetermining Δ_(AR1), where Δ_(AR1) is a value that takes expectedvariations in AR1 into account; automatically determining a timeAV_(cts), that is to be used instead of AV_(cts) during said capturethreshold search, with AV_(cts)<AR1−ER1−Δ_(AR1) but with the additionalcondition that AVM shall not be less than a predetermined minimum valuefor AV_(cts), wherein said minimum value is ≧0 even if ARI−ER1−Δ_(AR1)is less than said minimum value; and perform a capture threshold searchby using AV_(cts) instead of AV.
 34. A method according to claim 33,comprising including the following steps: automatically determining avalue AR2, where AR2 is a value which represents the time between apacing pulse to the first atrium and a subsequent event in the secondventricle, during a heart cycle when no pacing pulse is delivered to thesecond ventricle; determine automatically determining Δ_(AR2), whereΔ_(AR2) is a value that takes expected variations in AR2 into account;determine automatically determining AV_(cts) withAV_(cts)<AR2−VV_(cts)−ER2−Δ_(AR2) but with the additional condition thatAV_(cts) shall not be less than a predetermined minimum value forAV_(cts), wherein said minimum value is ≧0, even ifAR2−VV_(cts)−ER2−Δ_(AR2) is less than said minimum value; and perform acapture threshold search by using AV_(cts) instead of AV.
 35. A methodaccording to claim 34, comprising setting AV_(cts) as the smallest ofthe following values:AV,AR1−ER1−Δ_(AR1), andAR2−VV_(cts)−ER2−Δ_(AR2), but with the additional condition thatAV_(cts) shall not be less than a predetermined minimum value forAV_(cts), wherein said minimum value is ≧0, even if AR1−ER1−Δ_(AR1) orAR2−VV_(cts)−ER2−Δ_(AR2) is less than said minimum value.
 36. A methodaccording to claim 33 comprising employing a minimum value for AV_(cts)that is larger than 0 but less than 90 ms.
 37. A method according toclaim 36, comprising employing a minimum value for AV_(cts) that islarger than 30 ms but less than 70 ms.
 38. A method according to claim31 comprising: automatically determining a value PR1, where PR1represents the time between a sensed event in the first atrium and asubsequent event in the first ventricle, during a heart cycle when nopacing pulse is delivered to the first ventricle; determineautomatically determining Δ_(PR1), where Δ_(PR1) is a value that takesexpected variations in PR1 into account; automatically determining atime PV_(cts), that is to be used instead of PV during said capturethreshold search, with PV_(cts)≦PR1−ER1−Δ_(PR1) but with the additionalcondition that PV_(cts) shall not be less than a predetermined minimumvalue for PV_(cts) wherein said minimum value is ≧0, even ifPR1−ER1−Δ_(PR1) is less than said minimum value; and perform a capturethreshold search by using PV_(cts) instead of PV.
 39. A method accordingto claim 38, comprising: determine automatically determining a valuePR2, where PR2 is a value which represents a time between a sensed eventin the first atrium and a subsequent event in the second ventricle,during a heart cycle when no pacing pulse is delivered to the secondventricle; automatically determining Δ_(PR2), where Δ_(PR2) is a valuethat takes expected variations in PR2 into account; automaticallydetermining PV_(cts), with PV_(cts)≦PR2−V_(cts)−ER2−Δ_(PR2) but with theadditional condition that PV_(cts) shall not be less than apredetermined minimum value for PV_(cts) wherein said minimum value is≧0, even if PR2−VV_(cts)−ER2−Δ_(PR2) is less than said minimum value;and perform a capture threshold search by using PV_(cts) instead of PV.40. A method according to claim 39, comprising setting PV_(cts), as thesmallest of the following values:PV,PR1−ER1−Δ_(PR1), andPR2−VV_(cts)−ER2−Δ_(PR2), but with the additional condition thatPV_(cts), shall not be less than a predetermined minimum value forPV_(cts), wherein said minimum value is ≧0 even if PR1−ER1−Δ_(PR1) orPR2−VV_(cts)−ER2−Δ_(PR2) is less than said minimum value.
 41. A methodaccording to claim 18 comprising employing a minimum value for PV_(cts)that is larger than 0 but less than 60 ms.
 42. A method according toclaim 41, comprising employing a minimum value for PV_(cts) that islarger than 10 ms b Lit less than 40 ms.
 43. A method according to claim31 comprising performing the method on a human or animal being sufferingfrom congestive heart failure.
 44. A method according to claim 31comprising performing the method on a human or animal being sufferingfrom a bundle branch block.